1. Field of the Invention
The present invention relates primarily to an apparatus and method for repairing pipes and conduits, particularly relatively high-pressure pipes and conduits, such as a natural gas lines, water lines, and steam lines. More particularly, the invention is directed to an internal repair of a section of damaged, weakened, or leaking pipe or conduit, in which the section to be repaired is typically located in an inaccessible area, such as underground. Although conduit repair is an intended specific application of the invention, the apparatus and method disclosed has broader applicability and are contemplated to encompass the securing of a curable sealant to a surface and the general bonding of two surfaces together.
2. Background and Material Information
Conduit systems for conveying natural gas, water, and steam are typically located underground and, in general, are not easily accessible if repair or other maintenance is required after installation. Over a period of time, such conduit systems can become damaged, weakened, or can otherwise begin to leak, particularly at the joints between adjacent conduit sections, but also longitudinally along sections of the conduit. Thus, there can be a problem of ex-filtration of gas, water or steam from the damaged conduit sections. Additionally, old leaded joints in a water line must be isolated to prevent leaching of lead into drinking water.
Furthermore, in the repair of relatively high-pressure pipes and conduits, such as natural gas lines, water lines, and steam lines, which are utilized by utility companies, there is usually a need to effect the repairs in as short a time period as possible. Thus, there is a need to effect high strength repairs to such relatively high-pressure pipes and conduits quickly so that the utility lines can be returned to service in a relatively short period of time, such as less than one day.
Additional problems associated with such systems, and a number of previous repair methods and apparatuses are disclosed, for example, in U.S. Pat. Nos. 5,119,862 and 5,351,720. These patents, which disclose "No-Dig" or non-excavation repairs, utilize a sleeve or liner which is transported to the site of the weakened or damaged pipe in a coiled or partially coiled configuration. Once the repair liner is located in the necessary position at the site of the repair, internal pressure is applied to the sleeve by means of an inflatable bladder or other means, which causes the sleeve to begin to uncoil and expand in the direction of the "host" pipe to be repaired. The sleeve, which includes a gasket or sealing compound on its outer surface, reaches a slight over-expanded condition, whereby the liner compresses the gasket or sealing compound against the inner surface of the host pipe. The internal pressure is then reduced or removed and the sleeve is slightly recoiled, whereby overlapping edges of the sleeve become locked in place by virtue of complementary locking devices.
The methods and apparatus disclosed in the aforementioned patents are intended primarily for the repair of conduits that carry wastewater and other fluids that are not in an over-pressure environment. However, a high-pressure pipe, such as a natural gas line, a water line, or a steam line, also requires periodic repair, particularly for sealing against ex-filtration, i.e., against a leak of the fluid, such as natural gas, steam, or water, from the inside to the outside of the pipe. In addition, old leaded joints in a water line must be isolated to prevent the leaching of lead into drinking water.
The methods and apparatus disclosed in the aforementioned patents are useful for the repair of high-pressure pipes, although a particular problem, explained below, is posed. The size of these pipes is typically between 4 inches and 36 inches in diameter or even greater. Unlike an elastic compressible gasket or a polyurethane foam, e.g., which are usable for the repairs described in U.S. Pat. No. 5,351,720, high-pressure or over-pressure pipes and conduits require sealants that cure into a concrete-like hardness and which are not compressible. Such resins, unlike compressible or foam sealants, do not expand as they cure. Instead, they more or less retain their initial liquid volume. Thus, when an expandable repair sleeve having a curable sealant is positioned within a host pipe, expanded by the pressurizing device to compress the sealant into engagement with the inner surface of the host pipe, and subsequently the pressurizing device is retracted to allow the locking members of the inner sleeve to lock the sleeve into a tubular configuration, a gap is often formed when the inner sleeve contracts and pulls the curable sealant with it. This gap greatly reduces the strength of the repair, and depending on the location of the gap, the fluid conveyed within the conduit may ex-filtrate through the gap, or the pressure of the fluid may cause the repair sleeve to fracture in the area of the gap which would also allow the fluid to ex-filtrate through the repaired section.